This article describes the effect of friction welding conditions and aging treatment on the mechanical properties of type 7075-T6 aluminium alloy (A7075) friction welded joints. A7075 was joined by using a continuous drive friction welding machine with an electromagnetic clutch in order to prevent braking deformation during as rotation speed decreases. That is, it was welded by using the ‘Low Heat Input Friction Welding Method’ (LHI method) developed by the authors, in which heat input is lower than in the conventional method. The maximum joint efficiency at a friction pressure of 30 MPa was approximately 25%, and that at 90 MPa was approximately 64%. These joints were made without forge pressure. The low joint efficiency was due to the existence of non-joined regions at the welded interfaces. However, the welded joint had approximately 82% joint efficiency when the friction time was 0·5 s at a friction pressure of 90 MPa with a forge pressure of 180 MPa. The welded joint softened at the welded interface and its adjacent region. It had approximately 90% joint efficiency after aging for 730 days at room temperature (natural aging). It also had approximately 95% joint efficiency after aging for 48 h at 393 K (120°C), and had no softened region at the welded interface. The heat input of the welded joint with the LHI method could be decreased to approximately 50% of that with the conventional method. The LHI method has several advantages for A7075 friction welding; less heat input than with the conventional method, and light post-weld processing (machining, etc.) because the flash can be minimised.

The present paper describes the mechanical properties of Al-Mg aluminium alloy (A5052) friction welded joints. Two types of A5052 with different tensile properties were used, namely, H112 base metal with 188 MPa tensile strength and H34 with 259 MPa tensile strength. Similar metal specimens were joined using a continuous drive friction welding machine with an electromagnetic clutch to prevent braking deformation. That is, the joints were welded using the 'low heat input' friction welding method developed by the present authors, in which the heat input is lower than in the conventional method. An A5052-H112 joint produced using a friction speed of 27 . 5 s 21 , friction pressure of 30 MPa, friction time of 2 . 0 s (just after the initial peak torque), and forge pressure of 60 MPa had approximately 95% joint efficiency. It fractured at the welded interface and in the A5052-H112 base metal. To improve the joint efficiency, an A5052-H112 joint was produced at a forge pressure of 75 MPa, which was the same as the yield strength of the A5052-H112 base metal. It had 100% joint efficiency and fractured in the A5052-H112 base metal. In contrast, an A5052-H34 joint was made using a friction speed of 27 . 5 s 21 , friction pressure of 90 MPa, friction time of 0 . 3 s (just after the initial peak torque), and forge pressure of 180 MPa. It had approximately 93% joint efficiency and fractured in the A5052-H34 base metal. This joint also had a softened region at the welded interface and in the adjacent region. To improve the joint efficiency, an A5052-H34 joint was made at a forge pressure of 260 MPa, which was the same as the ultimate tensile strength of the A5052-H34 base metal. Although this joint had a slightly softened region at its periphery, it had approximately 93% joint efficiency. The failure of the A5052-H34 joint to achieve 100% joint efficiency is due to a slight softening at the periphery and the difference in the anisotropic properties of the A5052-H34 base metal between the longitudinal and radial directions.